When push-button tone station signaling service, such as TOUCH-TONE (registered service-mark of American Telephone and Telegraph Company) service, was first introduced to telephone subscribers, the demand for the service was insufficient to justify economically the provision of tone digit signal receiving circuitry and dial pulse circuitry in all of the originating call circuits of telephone offices. The problem was solved by providing two types of equipments, one to process dial pulses and the other to process tone digit signals and dial pulses. The two types of equipment were segregated by equipment locations in an office and dial pulse and tone signaling stations were assigned to the proper equipment locations in accordance with their authorized service. This, in one sense, was advantageous because it prevented a customer who had not subscribed to tone signaling service from installing an unauthorized tone signaling station and fraudulently using the service without paying for it.
As the demand for tone signaling service grew, however, the administrative and office equipment assignment tasks necessary to maintain segregation of the dial pulse and tone signal circuits became increasingly burdensome. It soon became evident that the practical solution to the problem was the provision of universal equipment which would operate both with dial pulse and tone signals. The result of this, however, is that subscribers served by certain telephone offices are able to defraud telephone companies by subscribing to dial pulse service while deriving the benefits of tone signaling service by installing their own tone signaling telepone stations.
The solution to the problem of preventing such fraud in offices that are vulnerable has been particularly elusive. Several schemes considered in the past directed toward blocking fraudulent tone signaled calls each involved the provision of some "class of dialing" indication which, of course, imposed some form of equipment or station assignment restriction and defeated the purpose of providing universal circuits. Other solutions involved extensive circuit modifications and proved too expensive to be justifiable. More recently, a proposed solution has been investigated which involves only the identification of stations from which tone signaled calls are placed, as opposed to blocking of the cells, and the subsequent verification, off-line, that the stations are authorized for such service. The major problem with this solution, however, is that in offices vulnerable to fraud, the only station identification available during originating calls are station equipment numbers, usually called line equipment numbers, which are generated by an office during call handling and which have no relationship to station directory numbers except via office cross-connections which are documented in office records. Service records identifying the services to which subscribers are entitled, on the other hand, are most conveniently maintained on a directory number basis. This solution thus contemplates the cumbersome steps of storing equipment numbers of stations from which tone signaled calls are placed, subsequently translating the station equipment numbers into directory numbers by means of office records and finally, searching station service records by directory number to verify whether or not the stations are authorized for tone signaling service.
Thus, a need exists for a simple and inexpensive method and structure for translating equipment numbers into directory numbers on certain types of originating calls.